In a number of applications there is a requirement for the provision of sinusoidal waveform signals to drive the modulation of other signals, or to modify transducer outputs. The use of sinusoidal waveform signals is preferred in a number of instances to minimise the number of harmonic components present in a signal other than its base frequency.
For example, Time of Flight (herein ‘ToF’) range imaging applications modulate both a light source for a scene and an imaging transducer with a common modulation frequency. Phase differentials are detected between the output source and received transducer signals to provide an indication as to the range to a particular object in the illuminated scene. An example of this type of time of flight image ranging technology is disclosed in the patent specification published as PCT Publication No. WO2004/090568.
Further modifications to these kinds of range determining camera systems have also been developed which apply a set of equal size increases of phase offsets to the light source being used. An original or source modulation signal is used to modulate the sensor output while the light transmitter output is modulated by the same original source modulation signal with a phase offset applied, allowing relative time of flight phase changes to be detected. Multiple phase measurements are made by integrating the output of the receiving sensor over a measurement time for each selected phase value applied. These sets of measurement are then used to compute and account for all the unknown variables contributing to the sensor reading.
Various other types of phase sensitive imaging applications have also been developed which require the provision of such modulation signals, such as for example, diffusion tomography, intensity modulated optical spectrometry (IMOS) and fluorescence lifetime imaging (FLM) applications.
The processing algorithms and mathematics employed in such applications often rely on the assumption that the modulation or sampling frequencies used are sinusoidal. However, in practice these expected sine waves are commonly provided by square waves which can be easily generated using off the shelf, low cost digital components.
Square waves include a number of higher order harmonic frequencies in their makeup. These high order harmonics can introduce a source of error in measurements of phase completed by these imaging systems.
It would therefore be of advantage to have improvements over the prior art which addressed the above issues or at least provided the public with an alternative choice.